Modernize worker task detail view

Summary: Make mobile-friendly and provide UI to cancel/retry tasks. Remove display of task data to arbitrary users, as it may be sensitive.

Test Plan:
{F22502}
{F22503}
{F22504}
{F22505}
{F22506}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2015

Differential Revision: https://secure.phabricator.com/D3854